In recent years, bag filters have been increasingly widely used in China's cement industry. Bag filters are used in many newly built cement production lines, and in the environmental protection renovation of old factories, the electric to bag scheme is also mostly adopted. While recognizing the advantages of bag filters, we should also fully recognize the shortcomings of bag filters, such as high equipment resistance, reduced dust removal efficiency, frequent damage to filter bags, and short service life of filter bags. These are mainly caused by unreasonable process design selection and equipment design, unreasonable selection of filter materials, poor quality of filter materials, and non-standard production, operation, and maintenance. In the process of cement production, there may be a phenomenon of high operating resistance of bag filters, which is very harmful, such as reducing dust removal efficiency, damaging filter bags, shortening filter bag life, unstable system operation, and high system power consumption.
Due to the different ways in which compressed air is used in pulse jet and gas box bag dust collectors, gas box bag dust collectors require higher pressure of compressed air than pulse jet. And the compressed air of the air box dust collector is sprayed into the chamber, causing a drastic change in the overall air pressure of the chamber to complete the dust cleaning. Under the premise of achieving effective dust removal, the size of the filter bag should not be too large, with a length generally not exceeding 3m and a diameter not exceeding 140mm; The length of the pulse jet dust collector filter bag can reach 6m, and the diameter can reach 170mm. Therefore, under the same filtration area, the volume and footprint of pulse jet dust collectors are relatively small.
In addition, in the coal powder industrial boiler system, the design and selection of bag filters need to comprehensively consider factors such as the frequency of boiler use by users, actual operating load of the boiler, user site, and capital investment. Pulse jet dust collector has a simple structure, low investment, and small footprint, making it suitable for use in small coal powder industrial boilers with low frequency of boiler use and infrequent high load operation. For coal powder industrial boilers that operate at high loads for 24 hours, the stability of furnace negative pressure is closely related to the overall normal operation of the boiler. During the dust cleaning process of the gas box bag filter, the dust cleaning airflow has little impact on the overall negative pressure of the main system. Even when maintenance and filter bag replacement are required, the system does not need to be shut down, which is beneficial for the stable operation of the coal powder boiler system.
The layout of the process equipment and production process of the bag filter equipment should be comprehensively considered based on the production plan, metal types, process level, factory site and plant conditions, and the dust removal technology, and all should have a suitable dust removal system. The design and core making departments with less pollution should be arranged on the downwind side of the low-frequency wind direction during non heating seasons in centralized heating areas, and on the downwind side of the low-frequency wind direction throughout the year in non centralized heating areas. The sand treatment and cleaning departments should be separated from other departments in the workshop using lightweight materials or solid walls. For large casting factories, the sand treatment and cleaning departments can be arranged in separate workshops. The pouring area should be arranged in a well ventilated location in the workshop. The processes of box closing, sanding, unboxing, sand cleaning, polishing, cutting, welding, etc. should be fixed at a fixed workstation or site to facilitate dust prevention measures. When cleaning workbenches for large-scale production are arranged in a continuous row, each workbench should be separated. When arranging process equipment, the reasonable layout of the process flow of the dust removal system, including the position of the dust hood, the laying of the air duct, the position of the platform, the setting of the dust collector, the centralized treatment of dust or sludge, etc., should provide the conditions of the plane position and three-dimensional space.
When the dust collector passes through the filter bag, small gas molecules pass through the gaps of the filter cloth with a dust layer attached, while large particles of dust are blocked from passing through. Due to gravity settling, they fall into the ash hopper. As the dust on the surface of the filter cloth continues to thicken, the resistance increases, and the gaps decrease, it becomes difficult for the airflow to pass through. When the dust layer accumulates to a certain extent, various cleaning methods need to be used to empty the filter bag.
The bag filter has the following characteristics:
1. Dust removal, the dust removal efficiency can reach above
2. Strong adaptability, able to handle different types of particulate matter, with a processing capacity that can be large or small
3. The operation has great flexibility, and when the inlet gas has a relatively high dust concentration, it has little effect on the dust removal efficiency
4. Simple structure, flexible use, easy to recycle dry materials, and no sludge treatment.
